Re: [Xen-devel] [PATCH 1/2] xen: xenbus_dev_frontend: Fix XS_TRANSACTION_END handling

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 02/07/2018 05:22 PM, Simon Gaiser wrote:
> Commit fd8aa9095a95 ("xen: optimize xenbus driver for multiple
> concurrent xenstore accesses") made a subtle change to the semantic of
> xenbus_dev_request_and_reply() and xenbus_transaction_end().
>
> Before on an error response to XS_TRANSACTION_END
> xenbus_dev_request_and_reply() would not decrement the active
> transaction counter. But xenbus_transaction_end() has always counted the
> transaction as finished regardless of the response.
>
> The new behavior is that xenbus_dev_request_and_reply() and
> xenbus_transaction_end() will always count the transaction as finished
> regardless the response code (handled in xs_request_exit()).
>
> But xenbus_dev_frontend tries to end a transaction on closing of the
> device if the XS_TRANSACTION_END failed before. Trying to close the
> transaction twice corrupts the reference count. So fix this by also
> considering a transaction closed if we have sent XS_TRANSACTION_END once
> regardless of the return code.
>
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.11
> Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent xenstore 
> accesses")
> Signed-off-by: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

(although I'd prefer Juergen to also take a look at this)

> ---
>   drivers/xen/xenbus/xenbus_dev_frontend.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c 
> b/drivers/xen/xenbus/xenbus_dev_frontend.c
> index f3b089b7c0b6..d2edbc79384a 100644
> --- a/drivers/xen/xenbus/xenbus_dev_frontend.c
> +++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
> @@ -365,7 +365,7 @@ void xenbus_dev_queue_reply(struct xb_req_data *req)
>                         if (WARN_ON(rc))
>                                 goto out;
>                 }
> -       } else if (req->msg.type == XS_TRANSACTION_END) {
> +       } else if (req->type == XS_TRANSACTION_END) {
>                 trans = xenbus_get_transaction(u, req->msg.tx_id);
>                 if (WARN_ON(!trans))
>                         goto out;
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